PHOENIX -- In part, the short video has the feel of a campaign ad: the strains of soft music, the iconic snapshots of rugged Arizona desert, the candidate earnestly engaged with her constituents.

Interspersed with the slick montage of photos and sound, though, is a video close-up of Rep. Gabrielle Giffords gazing directly at the camera, offering not a campaign promise but a goodbye, a thank-you message to her supporters in a voice that is both firm and halting.

"I have more work to do on my recovery," the congresswoman says at the end of the two-minute-long "A Message from Gabby," appearing to strain with all of her will to communicate. "So to do what's best for Arizona, I will step down this week."

Arizonans had to know in their hearts that this day was coming.

A bullet to the brain, from point-blank range, is a nearly impossible obstacle to overcome, even for a congresswoman known for pluckiness and fight. Giffords seemed to accept that reality in the video announcing her resignation from Congress, which also included a promise to return one day to her mission to help Arizonans.

The clip, posted to YouTube and on her Facebook page, pastes together 13 sentences into a fluid announcement. Giffords wears a bright red jacket eerily similar to the one she was wearing a year ago when she was nearly assassinated. She looks straight into the camera, almost begging the viewer to listen.

But the video also includes images of the 41-year-old struggling at rehab and walking along a leafy street with husband Mark Kelly with an obvious limp. And Giffords acknowledges that, at least for now, she isn't up to taking on a re-election challenge.

The announcement sets off not one but two election cycles to replace her. The first will be a special primary election that Gov. Jan Brewer must call sometime in April, with a general election in June to fill out the remainder of Giffords' term.

The second cycle will concern the regular full two-year term, with the primary scheduled for August and the general election in November.

In between, the 8th Congressional District that Giffords currently represents will change under redistricting. It will be remapped to cover most of the current district but renumbered as the 2nd Congressional District.

"We've got someone that's going to move in, hold that seat for the remainder of her (term,) and then we'll have people out there -- probably at the same time -- running for that seat ... with different lines," Brewer said. "So it will confuse some people."

Brewer said she spoke with Kelly before the announcement and understood the decision. "...As her husband said, they have sat, and they have discussed this, and that it would be the best thing for her and for her recovery," Brewer said. "And I indicated on the telephone with him that knowing Gabby and what she has accomplished in this last year in her recovery, who knows what's going to happen in the next two years."

The announcement came just over a year after a gunman opened fire at Jan. 8, 2011, meeting with constituents in front of a Tucson grocery store. Six people were killed, and Giffords and 12 others wounded.

Giffords' office said she will return to Tucson Monday to complete the meet-and-greet political event that erupted in the shooting. Among those attending will be some of the wounded, those who helped them and those who subdued the gunman.

At the time of the shooting, the Democrat had just eked out a razor-thin victory against a tea party candidate in her conservative-leaning district. She won a third term with less than 1 percent margin.

Many in Arizona believed she would be handed an easy victory if she chose to seek another term this year. But Giffords elected not to try.

"A lot has happened over the past year. We cannot change that," she said.

For days after the shooting, it was touch and go. A huge memorial grew in front of the Tucson hospital where she was fighting for her life.

Then, almost miraculously, just two weeks after she was shot, she was whisked off in a jet to a rehabilitation hospital in her astronaut husband's hometown of Houston.

Months of rehab began, with Giffords struggling to learn how to walk and talk again. Just over four months after she was shot, she flew to Florida to watch Kelly, an astronaut, pilot the nation's next-to-last space shuttle mission.

But she remained out of view.

Slowly, in carefully choreographed bits, she began to emerge. The first photos in June. Her surprise August appearance in Congress to vote to raise the federal debt limit. The first halting TV shots, just a few words at a time, then a more complex recording released in November.

Sunday's recording was slightly more elaborate, but it was not a campaign Q&A or an appearance before a tough interviewer.

She's clearly not yet ready for another run for Congress. But she said in Sunday's video that she's not done yet, an assessment that she shared with a small group of supporters in Tucson just hours after her announcement Sunday.

Jim Woodbrey, who was part of that group and a state Democratic Party official, called the meeting "very tough."

"It was Gabby's individual decision, and she was not in any condition to make that decision five months ago," said Woodbrey, a senior vice chairman of the state party.

And the congresswoman said in the video that she was getting better.

"Every day my spirit is high. I will return, and we will work together for Arizona and this great country," she said.